Abstract Cancer stem cells (CSCs) are those cells within a malignant tumor that can self-renew and initiate new tumors, with the ability to produce all the cell lineages that comprise the tumor. Recent studies have revealed that cancer treatments that target the tumor without addressing CSCs might reduce the tumor load but be unable to achieve a cure. Generation and maintenance of CSCs through genetic and epigenetic reprogramming is essential for tumor maintenance and resistance to therapy. Therefore, developing therapies targeted at CSCs is critical to achieving cures for cancer1. Yet the biology of CSCs, and particularly the process of cellular reprogramming, is still not well understood, in part because of the many mutations carried by these cells, only a few of which are deterministic. In order to develop a better understanding of the mechanistic underpinnings of adult cell dedifferentiation, we developed a zebrafish model that utilizes adult myocyte reprogramming in the context of muscle regeneration. Our model utilizes the lateral rectus muscle of the eye, which can recover from >50% myectomy by reprogramming the residual (i.e. “post-mitotic”) myocytes to reenter the cell cycle, remodel the extracellular matrix, proliferate, migrate and then redifferentiate into myocytes that reform a functional muscle (as determined by an optokinetic response). The proliferative burst of reprogrammed myocytes is particularly robust, with >70% of cells undergoing mitosis during the regeneration process. Such a robust in vivo model of cell dedifferentiation represents a unique opportunity to study the cellular, genetic and epigenetic processes involved. We find that the dedifferentiation process begins with activation of epigenetic regulators to remodel chromatin, followed by activation of autophagy to remodel the cytoplasm, followed by cell cycle reentry. Epigenetic changes include changes in DNA and histone methylation, along with activation of genes encoding transcription factors that are frequently found to be involved with oncogenesis, such as myc, jun, fos, and twist. A transcriptome analysis using deep sequencing reveals significant similarities between the genetic signatures of dedifferentiated zebrafish myocytes and human cancer cells. This analysis also identifies long non-coding RNAs that are induced early during the dedifferentiation process, and work is ongoing to annotate these lncRNAs with reference to human cancer. In summary, an in vivo zebrafish non-cancer model of cancer can provide unique mechanistic insights into the biology of CSCs. In addition, as an aquatic species this model is particularly well suited for drug screening, providing an innovative new approach to developing drugs that target reprogramming/dedifferentiating cells. Citation Format: Ke’ale Louie, Alfonso Saera-Vila, Phillip E. Kish, Alon Kahana. Zebrafish adult cell dedifferentiation as a noncancer model of cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2541.